A magneto generator is comprised of a magnet rotor, and a stator including an n-phase armature coil (n is an integer equal to or more than one) wound around an armature core having a magnetic pole portion facing a magnetic pole of the magnet rotor. Such a magneto generator is mounted to an internal combustion engine for driving a vehicle, and often used for charging a battery in the vehicle.
When the battery is charged with a rectified output of the magneto generator driven by the internal combustion engine, the battery does not start to be charged until a rotational speed of the engine increases to a certain extent and a no-load output voltage of the magneto generator exceeds a voltage across the battery. When a compact magneto generator is used, a rotational speed at which a battery starts to be charged is high, and thus the battery cannot be charged during a low speed rotation of the engine. For allowing the battery to be charged even during the low speed rotation of the engine, increasing the number of turns of the armature coil without changing a structure of the magneto generator can be considered, which, however, causes an insufficient output to be obtained from the magneto generator during a high speed rotation of the engine. For generating a sufficient output from the magneto generator during the low speed rotation of the engine, and also obtaining a sufficient output from the magneto generator during the high speed rotation of the engine, an armature coil with many turns needs to be wound by using a conductor with a large area, which increases a size and a weight of the magneto generator. A large magneto generator unpreferably increases a weight of the engine to cause poor fuel economy, or increases inertia of the engine to cause poor acceleration performance. Further, the large magneto generator cannot be mounted to a compact vehicle such as a motorcycle.
Thus, as described in Japanese Patent Laid-Open No. 2001-157497, a generating device has been proposed in which an output of a magneto generator is boosted by chopper control that interrupts a current supplied from a magneto generator through a rectifier circuit to a battery with a predetermined duty ratio in order to make up for an insufficient output in a low speed rotation range. Such chopper control can make up for the insufficient output in the low speed rotation range, and adjusting a duty ratio of on/off of an output current can adjust a charging current of the battery. For example, when a magneto generator is used whose rotational speed at which a battery starts to be charged without performing chopper control is 600 rpm, the rotational speed at which the battery starts to be charged can be reduced to, for example, 200 rpm by the chopper control.
As described in Japanese Patent Laid-Open No. 11-46456, a generating device has been proposed in which a circuit is provided that applies an AC control voltage to an armature coil of a magneto generator, and a phase angle of the AC control voltage is controlled to control an output of the magneto generator. The generating device described in Japanese Patent Laid-Open No. 11-46456 includes the magneto generator, a diode bridge full-wave rectifier circuit that converts an AC output of the magneto generator to a DC output, voltage storage means such as a battery or a capacitor connected across output terminals of the rectifier circuit, and an inverter circuit that converts the voltage across the voltage storage means into the AC control voltage and applies the AC control voltage to the armature coil of the generator. In the generating device, the voltage across the voltage storage means is converted into the AC control voltage having the same frequency as a voltage induced in the armature coil of the magneto generator, and the inverter circuit is controlled so as to apply the AC control voltage to the armature coil to change a phase of the AC control voltage, thus controlling the output of the magneto generator.
In the above described generating device, when the phase of the AC control voltage applied to the armature coil of the magneto generator is changed to an advancing side, an amount of magnetic flux acting on the armature coil can be reduced to restrain the output of the magneto generator. When the phase of the AC control voltage applied to the armature coil is changed to a lagging side, the amount of magnetic flux acting on the armature coil can be increased to increase the output of the magneto generator. Such control of the output of the magneto generator by applying the AC control voltage from the voltage storage means provided on a load side through the inverter circuit to the armature coil is herein referred to as “drive control” in the sense of controlling the output while driving the magneto generator from the load side.
Such drive control can change the phase angle of the AC control voltage to the lagging side to increase the output of the magneto generator during a low speed rotation. When the output of the magneto generator becomes excessive during a high speed rotation of the generator, the phase angle of the AC control voltage can be changed to the advancing side to restrain the output.
Such drive control can reduce a rotational speed at which a battery starts to be charged when the battery is charged with a rectified output of the magneto generator. For example, in a generating device using a magneto generator whose rotational speed at which a battery starts to be charged without drive control is 600 rpm, the rotational speed at which the battery starts to be charged can be reduced to 550 rpm by the drive control.
As described above, in the generating device using the magneto generator, the chopper control can increase the output of the magneto generator during the low speed rotation of the engine, and adjusting the duty ratio of the chopper control can adjust the output of the generator. However, the chopper control can increase the output of the generator only in the low speed rotation range of the engine, and the generation output cannot be increased in middle and high speed rotation range by the chopper control.
When the magneto generator is driven by an internal combustion engine for a vehicle, a problem occurs that the output of the generator becomes excessive during the high speed rotation of the engine. A short circuit type regulator has been used that short-circuits an armature coil when an output voltage of the generator exceeds a set value in order to prevent an output of a magneto generator from becoming excessive during a high speed rotation of an engine. However, when the short circuit type regulator is used, a high short circuit current passes through the armature coil in voltage control, and thus the armature coil unpreferably generates much heat.
The drive control of the magneto generator can prevent the output of the magneto generator from becoming excessive during the high speed rotation of the engine without using the short circuit type regulator, but an advantage of increasing the output of the magneto generator during the low speed rotation cannot be reasonably expected from the drive control.